Linear mixed-effect model of cSP.

This study aimed to investigate whether the cerebellum contributes to contraction-induced facilitation (CIF) of contralateral corticospinal excitability. To this end, repetitive cerebellar transcranial magnetic stimulation (TMS) was used to test whether it modulates CIF. Overall, 20 healthy young individuals participated in the study. Single-pulse TMS was applied to the left primary motor cortex to induce motor-evoked potentials (MEP) on electromyography of the right first dorsal interosseous (FDI) muscle to test corticospinal excitability. This measurement was conducted during contraction (10% maximum voluntary contraction [MVC]) and rest (0% MVC) of the FDI muscle. CIF, cerebellar brain inhibition (CBI), cortical silent period (cSP), and resting motor threshold (rMT) were measured before and after low-frequency repetitive TMS (crTMS) of the right cerebellum to downregulate cerebellar output. The CIF (contraction/rest of the MEP), CBI (conditioned/unconditioned MEP) during contraction, cSP, and rMT were not affected by crTMS. At rest, CBI was decreased. These findings indicated that the primary motor cortex function for the increase in corticospinal excitability was not affected by crTMS. This study contributes to our understanding of the role of the cerebellum in motor control. Additionally, it may inform decision-making for the site of cerebellar ataxia treatment using non-invasive brain stimulation.

本研究旨在探讨小脑是否参与对侧皮质脊髓兴奋性的收缩诱导易化（contraction-induced facilitation, CIF）。为此，本研究采用重复性小脑经颅磁刺激（transcranial magnetic stimulation, TMS）来验证其是否可调节CIF。最终共有20名健康青年受试者参与本研究。我们对左侧初级运动皮层施加单脉冲TMS，在右第一背侧骨间肌（first dorsal interosseous, FDI）的肌电图记录中采集运动诱发电位（motor-evoked potentials, MEP），以此评估皮质脊髓兴奋性。该检测分别在FDI肌肉收缩（10%最大自主收缩（maximum voluntary contraction, MVC））与静息（0% MVC）状态下开展。我们在右侧小脑接受低频重复性TMS（crTMS）以下调小脑输出前后，分别测量了CIF、小脑脑抑制（cerebellar brain inhibition, CBI）、皮层静息期（cortical silent period, cSP）以及静息运动阈值（resting motor threshold, rMT）。其中，CIF（收缩状态/静息状态下的MEP比值）、收缩状态下的CBI（条件化MEP/非条件化MEP比值）、cSP与rMT均未受crTMS影响；而静息状态下的CBI则出现降低。上述结果表明，crTMS并未影响介导皮质脊髓兴奋性升高的初级运动皮层功能。本研究有助于加深我们对小脑在运动控制中作用的理解，同时可为采用非侵入性脑刺激治疗小脑性共济失调的靶点选择提供参考依据。